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From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: robin.murphy@arm.com, will.deacon@arm.com, mark.rutland@arm.com
Cc: peterz@infradead.org, bigeasy@linutronix.de,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	Meng.Li@windriver.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/5] perf/arm-cci: Fix CPU hotplug race avoidance
Date: Tue, 5 Feb 2019 11:19:55 +0000	[thread overview]
Message-ID: <3ebabec2-5423-9aca-19aa-7cd96353efd6@arm.com> (raw)
In-Reply-To: <606ff8c3f7f35ccdcb4b52a49f692fb20e27359c.1549299188.git.robin.murphy@arm.com>

Robin,

On 04/02/2019 17:09, Robin Murphy wrote:
> The arm-cci probe logic faces a cyclic dependency wherein it has to pick
> a valid CPU to associate with before registering the PMU device, has to
> have the PMU state initialised before handling hotplug events in case it
> must be migrated, but has to have the hotplug notifier registered before
> the chosen CPU may go offline lest things get out of sync. The present
> code has tried to solve the races by using get_cpu() to pick the current
> CPU and prevent it from disappearing while the other two registrations
> are performed, but that results in taking mutexes with preemption
> disabled, which makes certain configurations very unhappy:
> 
> [ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004
> [ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0
> [ 1.983342] Preemption disabled at:
> [ 1.983353] [<ffffff80089801f4>] cci_pmu_probe+0x1dc/0x488
> [ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1
> [ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT)
> [ 1.983364] Call trace:
> [ 1.983369] dump_backtrace+0x0/0x158
> [ 1.983372] show_stack+0x24/0x30
> [ 1.983378] dump_stack+0x80/0xa4
> [ 1.983383] ___might_sleep+0x138/0x160
> [ 1.983386] __might_sleep+0x58/0x90
> [ 1.983391] __rt_mutex_lock_state+0x30/0xc0
> [ 1.983395] _mutex_lock+0x24/0x30
> [ 1.983400] perf_pmu_register+0x2c/0x388
> [ 1.983404] cci_pmu_probe+0x2bc/0x488
> [ 1.983409] platform_drv_probe+0x58/0xa8
> 
> However, we don't actually mind being preempted or migrated at this
> point; all that really matters is that whichever CPU we pick does not
> get offlined before we're done. Thus, do the robust thing and instead
> take the lock to inhibit CPU hotplug for the duration. This also
> revealed an additional race in assigning the global pointer too late
> relative to the hotplug notifier, so that gets fixed in the process.
> 
> Reported-by: "Li, Meng" <Meng.Li@windriver.com>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Thanks for fixing the issues.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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  parent reply	other threads:[~2019-02-05 11:20 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-04 17:09 [PATCH 0/5] Fix Arm system PMU hotplug issues Robin Murphy
2019-02-04 17:09 ` [PATCH 1/5] perf/arm-cci: Fix CPU hotplug race avoidance Robin Murphy
2019-02-05 10:10   ` Corentin Labbe
2019-02-05 11:19   ` Suzuki K Poulose [this message]
2019-02-10 20:43   ` Thomas Gleixner
2019-02-04 17:09 ` [PATCH 2/5] cpu/hotplug: Export __cpuhp_state_add_instance_cpuslocked() Robin Murphy
2019-02-04 17:09 ` [PATCH 3/5] perf/arm-ccn: Fix CPU hotplug race avoidance Robin Murphy
2019-02-05 11:38   ` Suzuki K Poulose
2019-02-10 20:44   ` Thomas Gleixner
2019-02-04 17:09 ` [PATCH 4/5] cpu/hotplug: Add locked variant of cpuhp_state_add_instance() Robin Murphy
2019-02-04 17:09 ` [PATCH 5/5] perf/arm_dsu: Fix CPU hotplug races Robin Murphy
2019-02-05 11:40   ` Suzuki K Poulose
2019-02-05 13:04     ` Robin Murphy
2019-02-05  9:25 ` [PATCH 0/5] Fix Arm system PMU hotplug issues Mark Rutland

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